Spheroidal free periods of the earth observed at eight stations around the world

Abstract

Spectral peaks corresponding to the spheroidal free periods of oscillation of the earth exist in the spectra of eight seismograms written at stations in different parts of the world shortly after the great Chilean earthquake of 22 May 1960. These data have been combined with those previously reported by various authors to obtain a very precise phase velocity vs period curve for Rayleigh waves in the period range of 200 to 3200 seconds. The observed spectral amplitudes lend some support to the assumption of a moving source, but they also indicate that the present theory is not adequate. The vertical motion is found to be symmetric with respect to reflections through the pole.